Hydrodynamic trimming method and device



. March 3,1970

v. VAN BIBBER I HYDRODYNIAMIC TRIMMING METHOD AND DEVICE Filed March 22. 1968 3 Sheets-Sheet 1 lr/amn %/2 52/ INVENTOR.

BY 0/1601 J P' M 4 AQas d-M 'yef March 3, 1970 v. H. VAN BIBBER 3, 8,2

HYDRODYNAMIC TRIMMING METHOD AND DEVICE Filed March 22, 1968 Y 3 Sheets-Sheet 2 March 3, 1970 V; H. VAN BIBBER nynnonmmxp TRIMMING umrnon AND DEVICE Filed larch 22, 1968 3 Sheets-Sheet 3 INVENTOR.

BY I il'un 4 00 United States Patent 3,498,248 HYDRODYNAMIC TRIMMIN G METHOD AND DEVICE Vordaman H. Van Bibber, 4201 Mariner Drive, Panama City, Fla. 32401 Filed Mar. 22, 1968, Ser. No. 715,336 Int. Cl. B63b 1/18; B64c 3/38, 9/00 US. Cl. 114-665 12 Claims ABSTRACT OF THE DISCLOSURE A method for trimming a watercraft while underway, including introducing a quantity of gas beneath the after hull of said watercraft; and apparatus for practicing the aforesaid method featuring a wedge selectively retractable into the bottom of the hull of said watercraft which is of minor dimensions in comparison to the hull dimensions of the watercraft.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention pertains to an improved construction of watercraft to permit the craft to assume the proper attitude in the Water with less expenditure of time or propelling power than heretofore possible.

In naval architecture it is well understood that each hull design has a particular preferred attitude at which it operates at optimum efiiciency, producing the maximum dynamic lift with the least drag. To obtain this preferred optimum attitude, a predetermined velocity must be reached. In order for the watercraft to reach this critical velocity, a given amount of power must, naturally, be expended. The precise amount of power required depends upon parameters beyond the scope of the naval architecture surrounding the initial hull design. Included among these parameters are such considerations as weight of the load supported by the hull and the specific distribution of the carried load. It is sufiicient, for purposes of explanation of this invention, to note that, for a given load and load distribution, a certain velocity must be imparted to said hull to make it assume its optimum attitude.

When a hull is operated in attitudes other than its optimum attitude, a greater amount of power is expended in propelling it. Further, a craft at attitudes other than its optimum attitude suffers in handling and maneuvering ability, such as to significantly reduce its operational safety.

As a hull of the planing type is propelled through the water, a pressure is developed as the Water is displaced by the hull. As expected, the greatest pressure occurs where the water intercepts the hull, the point of greatest transfer of kinetic energy. The pressure decreases aft of this point and eventually becomes negative due to the change of direction of the flow of water combined with the capillary adhesion of the water to the hull, termed hull wetting. This negative pressure, termed suction loading, counters the lift and is a primary cause of high trim angle operations. It is evidenced by the large pile up of water in a stern wave, or rooster tail, aft of the hull. This rooster tail is not, as frequently imagined by the layman, generated by propeller action, but by the nonlinear velocities imparted to the water by various incremental portions of the planing type hull being forced through the water. The magnitude of the suction force varies with hull design but, in general, is inversely proportional to the aspect ratio of the hullthat is, length to beamin such a manner as to favor, to a point, a wider hull. The magnitude of the suction load may be appreciated by considering some of the following observed planing hulls:

3,498,248 Patented Mar. 3, 1970 Forty foot cruiser: static weight 12 tons; suction load .24 ton or 2%.

Forty-two foot rescue vessel: static weight 13 tons; suction load 1.68 tons or 14%.

Sixty-three foot crash boat: static weight 30 tons; suction load 2.1 tens or 7%.

Eighty foot patrol boat: static weight 58 tons; suction load 3.5 tons or 6%.

From the foregoing, it is obvious that if the suction force, as represented by the above typical observations, can be overcome, a significant increase in performance will result. In a hydrofoil craft, this is especially true where the reduction in draft after take off is considerable.

This performance increase is obtained by the method and device of the invention by the expedient of placing the craft in its optimum attitude sooner and with the expenditure of a minimum of power. The primary parameter of attitude is the trim angle. For purposes of discussion of this invention, the trim angle shall be considered the angle the longitudinal axis of the watercraft makes with the undisturbed surface of the water. It should be observed, at this point, that those proficient in naval architecture recognize various refinements and components of this angle, but such a rigorous treatment is unnecessary for an understanding of this invention and, accordingly, will not be used. It should be obvious that the lower angles of trim present a lower equivalent flat plate area to the water and thereby produce a maximum of dynamic lift with a minimum of drag.

Accordingly, it is one of the primary objects of this invention to provide a method of general applicability and an improved structural arrangement to overcome the drag produced by hull wetting with a minimum expenditure of propulsion power.

A further object of this invention is the provision of a device which will assist a surface watercraft in obtaining its optimum attitude.

An additional object of this invention is the provision of a structure which will permit a hydrofoil craft to assume its designed take off attitude with a greater payload.

Another object of this invention is the provision of a device which will permit a hydrofoil watercraft to assume its normal attitude in a higher sea than would a similar hydrofoil craft not so equipped.

This invention also has as an object thereof the provision of a device to overcome hull wetting caused drag in a watercraft to permit said watercraft to assume its optimum attitude with a shorter surface run.

Another object of the instant invention is the provision of a device which, when incorporated as an integral part of the hull design of a planing type hull, permits a planing attitude to be obtained with the expenditure of less power than a similar hull without the benefit of said device.

This invention also has as its object an improved method and means for trimming a surface watercraft to its optimum trim angle by overcoming the drag produced by capillary wetting of the under portion of said watercraft.

Other objects and many of the attendant advantages will be readily appreciated as the subject invention becomes better understood by reference to the following detailed description, when considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a graphic representation of the drag versus speed for a typical hydrofoil watercraft;

FIG. 2 shows an embodiment of the device of the invention as installed on a typical watercraft;

FIG. 3 is a sectional view of the device of the invention taken along line 33 of FIG. 2;

FIG. 4 is a diagrammatic showing of the placement of another form of the invention on a hydrofoil;

FIG. isa sectional view of the form of the invention of FIG. 4 taken along lines 55 of FIG. 4;

FIG. 6 is a sectional view of the device of the invention taken along lines 66 of FIG. 4;

FIG. 7 is an illustration of the pressure distribution along the bottom of a planing type hull, equipped with a. retractable wedge according to the invention in a typical out-of-trim attitude;

FIGS. 8a through 80 show the transition of a planing type hull equipped with a retractable wedge according to the invention from an out-of-trim attitude to a properly trimmed planing attitude; and

FIG. 9 is a representation of the distribution of the pressure along the bottom of the hull of a planing craft, equipped with the device of the invention, when in a trimmed, planing attitude.

Referring now to FIG. 1, there is shown by curve 11 the drag and speed relationship of a hydrofoil type surface craft. It is noted that, as the velocity of the craft increases, the drag increases, until a point 12 has been obtained, at which point the slope of curve 11 changes, indicating a decrease in drag with an increase in velocity, until a point 13 is reached. From point 13 onward the drag is shown to increase as the velocity increases.

The marked decrease in drag with increased velocity in the region between points 12 and 13 is due to the hull of the hydrofoil craft rising from the water. For planing type hulls, without hydrofoils, the region of decreased drag is less pronounced, but of the same general configuration, as represented by the curve extension 14. The shaded portion of the hydrofoil curve 11 relates to the amount of work required to overcome the drag primarily occasioned by suction loading which may be, in part, due to the hull wetting phenomenon.

It has been established that the drag represented by the shaded portion can, in fact, be regarded as the result of bull wetting. This has been demonstrated by unwetting the hull at point 24 on the operational curve 11, whereupon the craft assumes a new trim angle and speed corresponding to point 25 on curve 11. For\ purposes of demonstration, a variety of agencies may be employed to accomplish this unwetting, including a charge of compressed gas timely discharged beneath the hull. However, in investigating this phenomenon, a simple, lightweight means has been devised which may be incorporated into established naval architecture designs without extensive modification thereof. This device is particularly suited to hydrofoil equipped craft where the reduction of draft is considerable and when rapid take-01f is a parameter of sufficient importance to merit serious consideration.

The device of the invention, by virtue of altering the water flow across the bottom of the hull, causes the hull of the craft to effectively unwet, and correlatively, to assume a planing attitude, in the case of a hull design of that type, or, in the instance of hydrofoils, to take off at a relatively low velocity. This permits the craft to assume its designed optimum attitude with the expenditure of less power, and to assume a proper trim with a shorter out-of-trim run, and gives rise to the name unwetting or take-off wedge used in describing the water flow modifying structureof the invention.

FIG. 2 illustrates one form of the device of the invention which has met with success. A wedge 15 is mounted along the bottom 16 extending from keel 17 to the side 18 of the boat. A similar wedge occupies a like posltion on the other side and, for purposes of explanation, may be regarded as an extension of wedge 15. The exact longitudinal location of the, wedge varies somewhat for different craft and must be determined for the particular craft in question. In general, the wedge 15 is located about two-thirds of the way toward the stern of the particular craft. Vessels with lower take-off speed and higher trim angles will have the wedge 15 located further aft than those with higher take-off speeds and larger trim angles. The size of wedge 15 is determined by conventional naval 4 architecture practice to produce the required vortex action at the speeds appropriate to the particular vessel to which the wedge is applied. In general, it is a few inches thick, and when actuated, it extends from 1 inch to 1% inches below the bottom of the hull.

Wedge 15 is only extended for very brief periods of time. When not extended, Wedge 15 is retracted into a housing 19. The wedge 15 is retracted and extended by expandable chamber motors 21 to which the wedge 15 is operatively attached by means of a connecting rod 22. Motor 21, which, if desired, may be mounted within housing 19, is supplied actuating fluid by means of fluid conduits 23, see FIG. 3, which are, in turn, connected to a suitable source of fluid pressure.

In some installations it may be desired to actuate the motors 21, without manual attention, by a speed responsive control system. Such a control system is particularly suited to high displacement hydrofoil craft where the necessary space and complexity of the control system would not impose undue design limitations, and where the benefits may be more practically realized.

When wedge 15 is lowered, a vortex is created just aft thereof. This suddenly created, transversely extending vortex modifies the water flow in the region of suction loading and is of sufficient magnitude to pull air from the water line area adjacent the side of the boat into the vortex, and therefore-beneath the boat. The air forms an interface layer along the bottom of the craft. This indrawn air breaks the surface tension and, thereby, destroys the capillary adhesion of the water in that region. The altered water flow redistributes the dynamic planing forces in this region. The action of the wedge thereby effectively unwets the hull and produces a rapid transition of the hull attitude to a properly trimmed condition. In the case of hydrofoil equipped craft, this corresponds to take off, or the hullrising from the water due to the lift of the hydrofoils.

It will be appreciated, from inspection of the drawings, that housing 19 may be incorporated as an integral portion of the structural framework of the hull of the watercraft.

Operation of wedge 15 may be accomplished by other means than expandable chamber motors 21, if desired. In small displacement craft actuation may be manually accomplished. However, electrical and combustion type power sources provide satisfactory drive energy sources for larger wedges if the expandable chamber motors 21 are not desired. Because the operation of the wedge is over such small intervals of time and only while getting underway, motive power sources used for other equipment on board may be utilized for actuating the wedge 15 with attendant modifications of said power sources to provide an'auxillary power take off.

It will be understood from the foregoing, again referring to FIG. 1, if the wedge 15 is actuated at point 24 on curve 11,- the unwetting action produced by wedge 15 will permit the craft to take off under the lifting action of the hydrofoil elements. The hydrofoil craft will, soon hydrofoils much'sooner than had the wedge 15 remained unactuated.

In order to reach the speed represented by point 25 on curve 11 without application of wedge 15, the hydrofoil craft must first pass through point 24 to reach point 12. It will be understood, for a stable speed to be maintained by the craft, the drag, shown by the plot of FIG. 1, must equal the propelling thrust. Thus, when point 12 is reached, the craft will rapidly accelerate along curve 11 through points 13 and 25 to obtain a speed corresponding to point 39 of curve 11. The reduction of power to permit the craft to assume a speed corresponding to point 25 must be then accomplished. Since considerable time may have elapsed since first passing through point 24 on curve 11, the hydrofoil craft will have traveled a correspondingly considerable distance at a greater than desired speed and in a less than optimum trim. The precise amount of time and distance covered is dependent upon the amount of power available and the loading of the craft. Nevertheless, when the draft of a hydrofoil craft prior to take off and the conjestion of todays watercourses is considered, the advantages of the present invention stand in marked contrast to prior art examples of hydrofoil naval architecture.

Referring to FIG. 4, there is shown a hull 26 of a hydrofoil craft. Hydrofoils 20 are shown mounted on suitable supports 30. A retractable wedge 27 of a modified configuration from that shown in FIGS. 2 and 3, is observed to be mounted toward the aft portion of hull 26. As shown in the simplified sectional representation of FIG. 5, wedge 27 extends from a housing 28. Like housing 19, housing 28 may be incorporated as a structural member of bull 26. A more detailed sectional drawing taken along lines 66 of FIG. 4 reveals that Wedge 27 is hollow so as to enclose an expandable chamber fluid motor 29. This motor is supplied an operating fluid under pressure (supplied by suitable means, not illustrated) via conduit 31, fluid coupling 32, and conduit 33. Wedge 27 is attached at its foreward end by a suitable hinge mechanism 34.

Although the construction of the wedge 27 and its operating mechanism as shown in FIGS. 4-7 is suitable for purposes of understanding applicants invention, other specific constructions may be used if of sound naval construction practice. One alternate embodiment, which has met with success, has the exandable chamber motors 29 mounted within the hull of the craft fitted with the device of the invention. The retractable wedge in the alternate embodiment is actuated by a bell crank mechanism which joins the retractable wedge to the driving power source. It is, of course, appreciated that the primary advantage of the illustrated embodiment is the absence of any watertight mechanical joints, which is obtained with some sacrifice in accessibility.

Again, it is to be emphasized, applicants wedge is quite small with regard to either the relative weights of the mechanism and the craft, or the relative size of the wedge and the planing surface of the hull. This is best understood by keeping the operative function of the device, i.e., the production of an abrupt discontinuity and accompanying altered flow pattern and low pressure vortex adjacent the surface of the hull for very short periods of time, clearly in view. Applicant is aware previous attempts in planing hull design have employed wedge sections of the hull that were caused, by suitable actuation means, to vary their angular position for the purpose of altering the hydrodynamics of the hull. This type construction alters the trim angle of the craft to which it is applied, but it does so with an increase in drag and requires an increased expenditure of power. None the less, the large pivoted planing surface has been used in such applications as the hull design of flying boat aircraft, where the out-oftrim surface run places the airfoil in a similar out-of-trim attitude and prevents the development of aerodynamic lift necessary for take-off. However, in conventional naval architecture the increased drag of the arrangement has limited its applicability.

Similarly attempts to overcome the stern wave, or rooster tail, by the use of planes extending aft of the stern. These planes extend the length of the craft upon which they are installed which and thereby tend to cause higher trim angles and correspondingly increased drag. These adverse affects in many cases offset the gains obtained by streamlining the waterflow across the stern of the watercraft. In some installations these protruding planes are shortened and made adjustable with respect to the axis of the watercraft. In many respects such as construction is analogous to the trim tab construction of aircraft and, like the trim tab, are dynamic force surfaces. Such constructions develop their corrective torque moments at the expense of a constant drag and increased equivalent flat plate or frontal area.

The device of the invention distinguishes from these prior art constructions by being of very steep angular slope and relatively small and light compared to the hull design. Accordingly, it does not contribute to the planing forces or other long duration hydrodynamic forces pertaining to the hull design on which it is installed. By way of example, a device installed experimentally on a twentytwo foot, 2,900 pound boat weighed 12.8 pounds. With a marginal power unit this boat reached a maximum speed, with full load, of 14.6 knots and exhibited a trim angle of twelve degrees. The device of the invention was operatedi.e., the wedge was extended-for a short period of time, which, in a series of runs, varied from .5 second to 1.1 seconds. Under the influence of the wedge, the boat changed its trim angle to eight degrees and increased its speed to seventeen knots. In every instance the boat maintained its new trim angle and speed after the wedge was retracted.

The results of the test runs with a planing type hull are qualitatively shown in FIGS. 7 through 9. FIG. 7 is a bottomside view of a planing type hull 35 propelled by screw 44 and incorporating a retractable unwetting wedge 36 in accordance with the teachings of the invention outlined above. The distribution of the planing force is shown by the shading, i.e., the denser the dots, the greater the pressure. As can be seen, the pressure pattern is uneffected by the retracted wedge 36, and the high pressure, or lift region, lies in a zone relatively far forward in relation to the center of gravity of the hull 35. The more slightly shaded zones show correspondingly less positive pressure, or lift. The zero without shading includes the center of the zone of zero and negative pressure and, as explained above, it is within this region that the suction force is active to cause the trim angle of the hull to exhibit its rearward bias.

For a more complete treatment of the pressure distribution of planing type hulls, see Lord, Lindsay; Naval Architecture of Planing Hulls; Cornell Maritime Press; Cambridge, Md.; 1954. Further, it should be noted that the pressure diagrams of FIGS. 7 and 9 are qualitative only and represent no particular vessel. Patterns similar to those shown may be obtained for any craft desired by utilizing the measuring technique, now regarded as standard, disclosed by Norman H. Jasper in an unclassified report entitled Dynamic Loading of a Motor Torpedo Boat (YP 110) During High Speed Operation in Rough Water; Department of the Navy; David Taylor Model Basin; Report Cl75: NS 715-007; September 1949 (copy available Library of Congress).

FIGS. 8a through show the hull 35 in two states of trim with the wedge retracted and an intermediate position of the hull 25 with wedge 36 extended. The indicated time passage is an attempt to graphically convey to the reader some measure of the remarkable transition effected by the operation of the wedge 36.

In operation of the equipped boat of FIG. 8a, the throttle 41 is manually set to some set power level. The throttle 41 is connected, via appropriate linkage 42, to a conventional power source 43. The mechanical output of power source 43 corresponding to the position of throttle 41 is carried to screw 44 via conventional coupling means. As the boat moves forward, it reaches a velocity which corresponds to the selected power output and trim angle. When this power setting is suflicient to propel the craft at a higher speed, but at a trim angle more compatible with the given crafts hull configuration, the unwetting wedge 36 is briefly applied. This wedge actuation alters the hydrodynamic forces in the region of suction loading, to permit a force distribution conducive to the desired trim. A vortex is also produced which unwets the hull, thereby destroying the capillary wetting adhesion in this area. The accompanying redistribution of forces on the hull of the craft moves the center of the dynamic planing force aft and thereby produces the desired change in trim.

In FIG. 8a, vector 37, which represents the center of lift or dynamic planing force corresponding to the distribution of dynamic planing force illustrated by FIG. 7, is diagrammatically shown. Vector 37 is, as expected, close to the center of gravity of hull 35, as represented by the conventional CG symbol. It should be understood that the figures are diagrammatic and do not illustrate the stern wave which always accompanies the out of trim operation and other waterline disturbance phenomtrim operation and other waterline disturbance phenomena.

In FIG. 812, it may be observed that wedge 36 is extended and the hull is in an intermediate position. Not evident in the drawing is the exhilarating burst of speed seldom associated with surface craft which accompanies the transition in trim of hull 35.

FIG. 80 depicts the hull 35 in its more-nearly-optimum attitude of trim. It is evident that the center of lift or dynamic planing force has moved aft, as evidenced by the relative position of vector 38 and the center of gravity of hull 35.

The pressure distribution of hull 35 in the final trim attitude, corresponding to FIG. 80, is shown in FIG. 9. Again, it should be noticed that retractedwedge 36 has no observable effect on the pressure distribution. As anticipated by the small angle between the water line 39 and hull 35 in the final trim attitude (FIG. 80), the pressure distribution of FIG. 9 is much more uniform than that of the out-of-trim attitude depicted in FIGS. 7 and 8a. The lighter shading, foreward of the zone of maximum pressure density, depicts contact between the hull and water surface'irregularities caused by the low trim angle of the yessel. The maximum lift occurs, as it obviously must, at the region of the maximum kinetic energy transfer, theleading zone of hull-water contact. This lift zone is, as shown, of' greater extent than in the out-of-trim condition.

Obviously, other embodiments and modifications of the subject .invention will readily come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing description and the drawings. It is, therefore, to be understood that this invention is not to be limited thereto and that said modifications and embodiments are intended to be included within the scope of the appended claims.

What is claimed is:

1. A method of changing the trim angle of a surface watercraft from a high, undesirable trim angle to a lower, more favorable trim angle comprising the steps of:

applying a propelling thrust insuflicient to obtain, but

sufiicient to maintain, said more favorable trim angle of said watercraft; disturbing the flow of water across the bottom of said watercraft in an area of low pressure foreward of the stern of said watercraft but aft of the center of gravity thereof in such a manner that the water flow across said bottom is redistributed to cause a vortex to be generated across said bottom; maintaining said disturbed water flow for a brief interval of time to cause said area of low pressure to unwet, thereby causing said surface watercraft to assume said more favorable trim angle; and

terminatingsaid water flow disturbing action when said more favorable trim angle has been obtained to thereby permit said surface craft to maintain said more favorable trim angle without further increase of said applied propelling thrust.

2. A surface watercraft hull trimming structure comprising:

a hull having a fixed bottom surface portion positioned to be acted upon by hydrodynamic forces as said watercraft is propelled forward to effect a desired angle of trim of said watercraft and upwardly extending side wall portions joins to the bottom surface portion of said hull;

a recess disposed in said bottom surface portion of said hull which is open at the lower side thereof, said recess extending transversely substantially the entire distance across said bottom surface portion and longitudinally extending a predetermined distance which is small in comparison to both the transverse extension thereof and the length of said hull;

a wedge member having surfaces of small area in comparison to said bottom surface portion and being retractably mounted within said recess; and

motor means operationally connected to said wedge member for the selective moving thereof in and out of said recess in such manner that when it is retracted therewithin the waterflow across the aforesaid bottom surface portion of said hull is substantially uninterrupted andwhen it is extended from said bottom surface portion of said hull it effectively interrupts the water flow thereat, so as to produce a vortex which neutralizes the suction loading on said bottom surface portion aft of said recess.

3. A surface watercraft hull trimming stiucture according to claim 2 further comprising:

support means attached to said hull projecting downwardly therefrom; and

hydrofoil means mounted on said support means to provide lifting support for said watercraft.

4. A surface Watercraft hull trimming structure according to claim 2 wherein said motor means is mounted Within the confines of said hull.

5. A surface watercraft hull trimming structure according to claim 3 wherein said motor means is mounted Within the confines of said hull.

6. A surface watercraft hull structure according to claim 2 wherein said motor means is mounted within said recess. r

7. A surface water craft hull structure according to claim 3 wherein said motor means is mounted within said recess.

8. A surface watercraft hull structure according to claim 2 wherein said wedge member is mounted so as to telescopically retract within said recess.

9. A surface watercraft hull structure according to claim 3 wherein said wedge member is mounted so as to telescopically retract within said housing means.

10. A surface watercraft according to claim 2 wherein said wedge member is mounted so as to pivotally retract within said recess.

11. A surface watercraft according to claim 3 wherein said wedge member is mounted so as to pivotally retract within said recess.

12. A surface watercraft hull trimming structure according to claim 2 in which said motor means comprises a fluid actuated expandable chamber motor.

References Cited UNITED STATES PATENTS 2,347,841 5/1944 Parker 114-665 2,859,004 11/1958 Lopiccolo 244--42.6 3,026,839 3/1962 Fridge 114-665 3,159,131 12/1964 Frederick 1l466.5 3,357,390 12/1967 Wray 114-665 ANDREW H. FARRELL, Primary Examiner US. Cl. X.R. 24442 

